The invention relates to a method for transmitting data to at least one listening subscriber of an existing group call immediately after switching talkers within a mobile radio system including at least one anchor mobile services switching center and at least one relay mobile services switching center to which in each case at least one base station system is connected, wherein, for changing the talker function from a first subscriber to a second subscriber of the existing group call, an uplink group call channel is allocated to the second subscriber.
Digital mobile radio systems including radio cells are known, for example mobile radio systems based on the GSM (Global System for Mobile Communication) standard via which, in particular, voice group call services (VGCS), voice broadcast service (VBS) can be provided. Such group call services in which in each case a group call is directed to a group of radio subscribers (“subscribers” for short) are defined, for example, in the 3GPP TS 43.068 and 43.069 standards, the subscribers being talking and/or listening users of a mobile communication terminal, for example.
In this context, the subscribers of a group are located in a group call area formed from at least one radio cell, in which the subscribers of the group, controlled via at least one anchor mobile services switching center and possibly further relay mobile services switching centers, can move freely during an existing group call.
The anchor mobile services switching center is in each case connected to the relay mobile services switching centers to which in each case at least one base station system is connected. A base station system generates at least one coverage area in the form of a radio cell. The individual, partially overlapping radio cells form in their totality the entire coverage area of a mobile radio system. In this arrangement, the anchor mobile services switching center is provided for handling and maintaining a group call and the relay mobile services switching center is responsible for controlling and administering the radio cells of the group call area which have not been allocated already to the anchor mobile services switching center.
To identify the potential subscribers of a group call, a special group address information item (group ID) is allocated to them within the mobile radio system, which, for accepting a new group subscriber, is transmitted to them via a short message service (SMS) message. This procedure is known, among other things, by the term OTA (over the air) activation. For this purpose, for example, an OTA server unit is provided in the mobile radio system which implements the generation and updating of current subscriber lists of the group call and the generation of connection parameters required for a group call.
The setting up of a group call according to 3GPP specifications 43.068 and 43.069 requires that a common group call channel is set up for talking and listening users of a communication terminal. For this purpose, a group call is initiated via a so-called dispatcher, i.e. a group subscriber who has authorization to talk within an existing group call even without allocation of the talker function.
The group call channel includes a downlink group call channel and an uplink group call channel, these being set up to each radio cell of the group call area for the respective group. In this context, the uplink group call channel is exclusively provided for the talking subscriber of a group call, whereas all listening subscribers of a group call receive the group call data or group application data, transmitted via the uplink group call channel to the mobile radio system, via the common downlink group call channel.
After the setting up of a group call as described, the uplink group call channel is first allocated to the dispatcher as talker. To change the talker function within an existing group call, the dispatcher releases the uplink group call channel (uplink free message) and informs the other group subscribers about the release of the uplink group call channel. Thereafter, a group subscriber can claim the talker function for himself by requesting the uplink group call channel according to a standardized uplink request method. After a request initiated by a group subscriber taking over the talker function, the uplink group call channel, and thus the talker function, are allocated to him.
In typical group calls, the talk times per talker are very short, seen statically, so that the switching of the talker function from a first subscriber or a first user of a first communication terminal to a second subscriber or to a second user of a second communication terminal, respectively, within an existing group call connection should take place within a very short time. This should take place within a very short time, for example less than 500 ms, particularly if the new talker would like to send a text message to the earlier talker.
However, known signaling protocols in mobile radio systems already existing have a number of time-intensive signaling steps and currently offer no possibility of sending out text data (see SMS service according to 3GPP TS 23.040). In particular, it is not possible for subscribers involved in the switching of talkers to exchange text data with one another.